I think that for doing this we need things like vegetation, because only walk and see mountains and water it's not fun... This should be implemented, but i honestly think that we have other priorities.

It wouldn't be as cool as it sounds, because current LOD is still not enough to accurately simulate environment at this scale. Planets would feel really, really empty. To be fair, I cannot see the point of making SE some sort of Minecraft/KSP clone. It exceeds both in creating epic scenery, which shouldn't be abandoned for game mechanics.